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Oil Sands Environmental Management Bibliography

The Cumulative Environmental Management Association (CEMA)partnered with the Oil Sands Research and Information Network (OSRIN) to create the new Oil Sands Environmental Management Bibliography, which includes documents relevant to the environmental management of oil sands development in Alberta. The majority of the documents focus on the mineable oil sands in the Athabasca deposit, though some documents relate to in-situ developments. This bibliography was last updated in November 2014.

Metabolism of BTEX and naphtha compounds to methane in oil sands tailings

Year of Publication: 2007

Abstract:
Naphtha, comprising low molecular weight aliphatics and aromatics (C3-C14), is used as a diluent in processing of bitumen from oil sands. A small fraction (<1%) is lost to tailings waste and incorporated into mature fine tailings (MFT). BTEX (benzene, toluene, ethylbenzene, and xylenes) and whole naphtha were assessed for biodegradation under methanogenic conditions using MFT from an oil sands tailings settling basin. MFT spiked with 0.05-0.1% w/v of BTEX compounds produced up to 2.1 (+/-0.1) mmol of methane during 36 weeks of incubation. Metabolism of 0.5-1.0% w/v naphtha in MFT yielded up to 5.7 (+/-0.2) mmol of methane during 46 weeks of incubation. Gas chromatographic analyses showed that BTEX degraded in the sequence: toluene > o-xylene > m- plus p-xylene > ethylbenzene > benzene. Only 15-23% of whole naphtha, mainly n-alkanes (in the sequence: nonane > octane > heptane) and some BTEX compounds (toluene > o-xylene > m-xylene), was metabolized. Other naphtha constituents, such as iso-paraffins and naphthenes, remained unchanged during this period. These results suggest that the microbial communities in the MFT can readily utilize certain fractions of unrecovered naphtha in oil sands tailings and support methanogenesis in settling basins. Current study findings could influence extraction process, MFT management, and reclamation options.

Metal removal from oil sands tailings pond water by indigenous micro-alga

Year of Publication: 2012

Abstract:
This paper reports the removal of ten target metals of environmental concern ((53)Cr, Mn, Co, (60)Ni, (65)Cu, (66)Zn, As, (88)Sr, (95)Mo, and Ba) from oil sands tailings pond water. The organism responsible for removal was found to be an indigenous green micro-alga identified as Parachlorella kessleri by sequencing of the 23S rRNA gene. P. kessleri grew in tailings pond water samples taken from two oil sands operators (Syncrude Canada Ltd. and Albian Sands Energy Inc.), and enriched with low (0.24 mM NO(3)(-) and 0.016 mM PO(4)(-3)) and high (1.98 mM NO(3)(-) and 0.20mM PO(4)(-3)) concentrations of nutrient supplements (the most realistic scenario). The removal of (60)Ni, (65)Cu, As, (88)Sr, (95)Mo, and Ba from Syncrude tailings pond water was significantly enhanced by high concentrations of nitrogen and phosphorus, whereas the high nutrient concentrations adversely affected the removal of Co, (60)Ni, As, (88)Sr, and Mo in samples of Albian tailings pond water. Based on ANOVA two-factor analysis, higher nutrient concentration does not always result in higher metal removal, and TPW source must also be considered.

Metal removal from tailings pond water using indigenous micro-alga

Year of Publication: 2010

Abstract:
This paper reports the removal of ten target metals of environmental concern ((53)Cr, Mn, Co, (60)Ni, (65)Cu, (66)Zn, As, (88)Sr, (95)Mo, and Ba) from oil sands tailings pond water. The organism responsible for removal was found to be an indigenous green micro-alga identified as Parachlorella kessleri by sequencing of the 23S rRNA gene. P. kessleri grew in tailings pond water samples taken from two oil sands operators (Syncrude Canada Ltd. and Albian Sands Energy Inc.), and enriched with low (0.24 mM NO(3)(-) and 0.016 mM PO(4)(-3)) and high (1.98 mM NO(3)(-) and 0.20mM PO(4)(-3)) concentrations of nutrient supplements (the most realistic scenario). The removal of (60)Ni, (65)Cu, As, (88)Sr, (95)Mo, and Ba from Syncrude tailings pond water was significantly enhanced by high concentrations of nitrogen and phosphorus, whereas the high nutrient concentrations adversely affected the removal of Co, (60)Ni, As, (88)Sr, and Mo in samples of Albian tailings pond water. Based on ANOVA two-factor analysis, higher nutrient concentration does not always result in higher metal removal, and TPW source must also be considered.

Metals and polycyclic aromatic hydrocarbons in colonial waterbird eggs from Lake Athabasca and the Peace-Athabasca Delta Canada

Year of Publication: 2011

Abstract:
In 2009, aquatic bird eggs from a variety of species were collected from three sites in northern Alberta, Canada. Two sites were located in receiving waters of the Athabasca River, which drains the oil sands industrial region north of Fort McMurray, Alberta. The third site, located on the Peace River, was remote from the influence of the Athabasca River. Levels of mercury, arsenic, and polycyclic aromatic hydrocarbons (PAHs) were measured in the eggs along with nitrogen stable isotopes (δ¹⁵N) as an indicator of bird trophic position. Levels of As and PAHs in eggs were low, whereas Hg was measureable in all samples. Egg Hg levels increased with δ¹⁵N values (a proxy of food web trophic position); however, some eggs exhibited Hg levels greater than expected based on trophic position. These eggs were from sites in receiving waters of the Athabasca River, namely, Mamawi Lake and Egg Island. Levels of Hg in egg pools were correlated with naphthalene levels, perhaps indicating a common source of contamination. Temporal comparison of Hg levels in California gull (Larus californicus) eggs from the Lake Athabasca colony indicated that egg Hg burdens increased 40% from 1977 to 2009. More research is required to evaluate temporal trends in levels of environmental contaminants and to identify sources.

Meteorological factors affecting ambient SO2 concentrations near an oil sands extraction plant

Year of Publication: 1980

Abstract:
Occurrences of maximum 0.5 h hour ground level measurements of SO2 near a point source are related to the meteorological processes at the time such that a cause analysis of the occurrences is established. Measurements, from a 10 station, continuous air quality monitoring network, range from 0.12 to 0.65 ppm and are taken over a 2 year period, from 1976 to 1978, in the Alberta Oil Sands Environmental Research Program (ASOERP) study area. Point source emissions during this period average 125 tonnes sulphur per day (125 MTS/day). Meteorological data used in the analysis consist of local minisonde temperature profiles, synoptic weather maps, wind and temperature data from a 152 m tower, data from a nine station climatology network, local measurements of incoming solar radiation, and airport weather office and regional radiosonde observation (RAOB) data. Analysis of ambient monitoring measurements indicates that SO2 concentrations can be grouped into case data sets that suggest an influence of specific synoptic weather systems. Results of the analysis show that the soconcentrations are caused by arctic air mass inversions occurring in the spring, fall, or winter seasons. Frontal inversions with moderate winds, and convective mixing have also been identified as contributing factors for other cases, occurring in the spring. Comparison of observed and calculated ground level concentrations is made using Alberta Environment's dispersion program. The two-layer model predicts within a factor of 2 for the trapping cases. The unlimited mixing cases only predict to within a factor of 10 to 100.

Meteorology and air quality winter field study in the AOSERP study area March 1976

Authors Fanaki, F.
Year of Publication: 1978

Abstract:
In March 1976, the first in a series of intensive field studies was carried out in the Alberta Oil Sands Environmental Research Program study area in northeastern Alberta to examine the fine structure of the atmosphere and dispersion characteristics under winter conditions. The study comprised several co-ordinated sets of measurements over a two week period. These included: minisonde flights, tethersonde vertical profiles, acoustic sounder and delta-T sonde profiles, correlation spectrometer and ground level sulphur dioxide measurements, plume rise photography and background air and precipitation chemistry. Plume dispersion measurements made by aircraft were co-ordinated with the study and are reported in a separate publication. All measurements, except those for background air chemistry, were made within 20 km of Mildred Lake taking in the present oil sands processing facility of Great Canadian Oil Sands Ltd. and the future production site of Syncrude Canada Ltd. The study was successful in identifying unique features of the winter environment of the area such as diurnal formation and breakup of inversion layers, the effects of the river valley on circulation patterns, plume characteristics, pollutant deposition patterns in the snowpack and background levels of gases and particulates.

Methane emissions from oil sand tailings by microbial metabolism of hydrocarbons

Authors Siddique, T., & Foght J.
Year of Publication: 2011

Abstract:
Enormous volumes of tailings produced during bitumen extraction from oil sands ores are stored in settling basins/tailings ponds. The current inventory of tailings in northern Alberta, Canada exceeds 850 million m3. Biogenic methane emissions have been observed from the surfaces of tailings ponds and about 40 million L of methane day-1 was estimated from a single tailings pond (Mildred Lake Settling Basin) in 1999. This research project was initiated to investigate the source and mechanism of methane emission from the oil sands tailings ponds. The mature fine tailings (MFT) were collected from Syncrude Canada Ltd. and Shell Albian Sands tailings ponds and investigated for methanogenic biodegradation of solvent hydrocarbons that are used in the bitumen extraction process and the residual fractions of these solvents that are present in the tailings deposited in the tailings ponds. Our laboratory experiments have shown that only short-chain n-alkanes (C6-C10) and certain monoaromatics (BTEX) present in C3-C14 range hydrocarbons entrained in Syncrude tailings are readily biodegraded by the indigenous microorganism in the tailings ponds to produce methane. In contrast, a very long acclimation period has been observed for indigenous microbes to degrade long-chain n-alkanes (C14-18) and branched alkanes such as 2-methylpentane. Experiments are in progress to monitor the degradation of these recalcitrant compounds. The molecular analysis of 16S rRNA genes revealed that different microbial communities are involved in the degradation of different groups of petroleum hydrocarbon in oil sands tailings. Understanding the mechanism(s) of biogenic methane production and predicting emissions from oil sands tailings ponds are important objectives for effective management of tailings and greenhouse gas emissions.

Methane production in oil sands tailings under nitrogen-depleted condition

Year of Publication: 2013

Abstract:
Surface mining for bitumen extraction results in production of tailings that are deposited into large ponds. Tailings in the ponds support diverse microbial communities capable of metabolizing organic compounds and producing biogenic gases (methane, CH4 and carbon dioxide, CO2). Because of low endogenous concentrations of bioavailable nitrogen (N), tailings ponds might be deficient in available N (NO3-/NH4+). This study examined the potential of N2-fixation mediated methanogenic degradation of citrate and petroleum hydrocarbons in oil sands tailings under N-depleted conditions. Anaerobic primary cultures were set up with available N or N-deficient medium under N2 headspace using mature fine tailings (MFT) and amended with citrate as a carbon source. Citrate was metabolized to CH4 under both N available and deficient conditions suggesting N2-fixation mediated degradation of citrate. Acetylene reduction assay and incorporation of 15N2 stable isotope into microbial biomass supported N2-fixation during citrate metabolism.

Methanogenesis and fine tailings waste from oil sands extraction: A microcosm-based laboratory examination

Year of Publication: 2000

Abstract:
In the past decade, biogenic methane production in the fine tailings pond of Syncrude Canada Ltd. has increased markedly. This study addressed the questions: what started methanogenesis; what are the substrates for methanogenesis; and how long will methanogenesis occur? All the fine tailings produced methane but the organic compounds leading to methanogenesis could not be identified. Phenol, p -cresol and m -cresol stimulated methanogenesis but o -cresol, toluene, phenanthrene, anthracene, hexadecane and naphthenic acids did not. Mixtures of the naphthenic acids were toxic to the consortium. In the fine tailings, methanogens and sulfate-reducing bacteria co-exist but the precise relationship between the two populations could not be determined. Bacterial competition stimulated by the addition of nitrate and sulfate inhibited methanogenesis. Fine tailings samples produced between 0.10 to 0.25 mL CH 4 /mL tailings in batch methanogenesis monitored for over a year. Methanogenesis was a finite process and slowed after substrates were depleted.

Methanogenesis in oil sands tailings: An analysis of the microbial community involved and its effects on tailings densification

Authors Li, C.
Year of Publication: 2010

Abstract:
Densification of tailings slurries to mature fine tailings (MFT) is important in the oil sands industry for tailings inventory reduction, pore water recovery and tailings reclamation. The cause of methane release from the tailings pond of Shell Albian Sands (Albian) and the effects this process has on densification of Albian tailings was investigated. Citrate, added to tailings with polyacrylamide and hydrocarbon-diluent, was identified as the methanogenic substrate. Bacterial and Archaeal 16S rRNA gene sequences in Albian MFT were dominated by matches to Rhodoferax, some Clostridia and sulfate-reducing bacteria, and acetoclastic methanogens. Citrate-, diluent-, and polyacrylamide-amendments to Albian MFT did not cause a microbial shift over a 10-month laboratory incubation period. A potential pathway for microbial methane production in Albian MFT is proposed. Methane production and release from citrate-amended Albian MFT correlated to accelerated densification. Though diluent and polyacrylamide did not affect methanogenesis, they potentially affect gas bubble formation and release.

Methanogenic potential of tailings samples from oil sands extraction plants

Year of Publication: 2002

Abstract:
Approximately 20% of Canada’s oil supply now comes from the extraction of bitumen from the oil sands deposits in northeastern Alberta. The oil sands are strip-mined, and the bitumen is typically separated from sand and clays by an alkaline hot water extraction process. The rapidly expanding oil sands industry has millions of cubic metres of tailings for disposal and large areas of land to reclaim. There are estimates that the consolidation of the ma- ture fine tails (MFT) in the settling ponds will take about 150 years. Some of the settling ponds are now evolving microbially produced methane, a greenhouse gas. To hasten consolidation, gypsum (CaSO4·2H2O) is added to MFT, yielding materials called consolidated or composite tailings (CT). Sulfate from the gypsum has the potential to stimu- late sulfate-reducing bacteria (SRB) to out-compete methanogens, thereby stopping methanogenesis. This investigation examined three MFT and four CT samples from three oil sands extractions companies. Each was found to contain methanogens and SRB. Serum bottle microcosm studies showed sulfate in the CT samples stopped methane production. However, if the microcosms were amended with readily utilizable electron donors, the sulfate was consumed, and when it reached approximately 20 mg/L, methane production began. Some unamended microcosms were incubated for 372 days, with no methane production detected. This work showed that each MFT and CT sample has the potential to become methanogenic, but in the absence of exogenous electron donors, the added sulfate can inhibit methanogenesis for a long time.

Methanogens and sulfate-reducing bacteria in oil sands fine tailings waste

Year of Publication: 2000

Abstract:
In the past decade, the large tailings pond (Mildred Lake Settling Basin) on the Syncrude Canada Ltd. lease near Fort McMurray, Alta., has gone methanogenic. Currently, about 60%–80% of the flux of gas across the surface of the tailings pond is methane. As well as adding to greenhouse gas emissions, the production of methane in the fine tailings zone of this and other settling basins may affect the performance of these settling basins and impact reclama- tion options. Enumeration studies found methanogens (105–106 MPN/g) within the fine tailings zone of various oil sands waste settling basins. SRB were also present (104–105 MPN/g) with elevated numbers when sulfate was avail- able. The methanogenic population was robust, and sample storage up to 9 months at 4°C did not cause the MPN val- ues to change. Nor was the ability of the consortium to produce methane delayed or less efficient after storage. Under laboratory conditions, fine tailings samples released 0.10–0.25 mL CH4 (at STP)/mL fine tailings. The addition of sul- fate inhibited methanogenesis by stimulating bacterial competition.

Method for extraction and multielement analysis of Hypogymnia physodes samples from the Athabasca oil sands region

Year of Publication: 2013

Abstract:
A microwave-assisted digestion technique followed by ICPMS analysis was used to measure concentrations of 43 elements in Hypogymnia physodes samples collected in the Athabasca Oil Sands Region (AOSR) of northern Alberta, Canada. Analysis of multiple Standard Reference Materials, replicate samples and digestion blanks indicate that 34 elements were routinely quantifiable in small samples of lichens (25-30 mg) from the AOSR. Analysis of As and Se was performed by dynamic reaction cell ICPMS techniques to minimize polyatomic interferences and improve detection limits. Data from 121 sampling locations show that concentrations of many elements are higher (factors of 1.5-3) near the oil sands operations (i.e., within 50 km) than further away (i.e., beyond 50 km). Statistical analysis shows that many of the 34 elements (particularly the Rare Earth Elements) are highly correlated, but others only have weak correlations with a few other elements. Linear regression of element concentrations versus Al indicates a range of behavior across elements that likely reflect multiple accumulation processes. Comparison with previous studies of Hypogymnia physodes shows that elemental concentrations within the AOSR are generally comparable but often towards the lower end of those reported for remote and background areas of the northern hemisphere. Sb and Pb concentrations, in particular, are among the lowest reported for Hypogymnia physodes.

Methodology for geomorphic assessment of alluvial channels in oil sands region - a case study

Authors Ashiq, M., & Ehsan S.
Year of Publication: 2011

Abstract:
This paper explains procedure devised and used for the design of dynamic system for geomorphic studies in the Oil Sand Regions (northern Alberta, Canada), comprising Muskeg, and deals with geomorphic investigation, scientific issues and technical complexities, approach and methodology. Conventional approaches for design of reclamation drainage systems often provide rigid, non- erodible drainage facilities that are designed to handle specific extreme flood events. The alternative to rigid systems designed for specific extreme events is a dynamic system capable of accommodating evolutionary changes without accelerated erosion or unacceptable environmental impacts, a geomorphic approach. Development of this approach requires a comprehensive field investigation, afterward analysis and development of design equations for the design of streams to restore them back into pre- excavation form - this study provides a systematic procedure to the solution.

Metrics for assessing fisheries productivity and offsetting strategies under Canada’s New Fisheries Act

Year of Publication: 2014

Abstract:
The Alberta oil sands region contains one of the world’s largest oil deposits, estimated at 1.7 trillion barrels. Development in this region can have negative effects for aquatic species, governed under Canada’s Fisheries Act. The Fisheries Act allows the possibility for offsetting losses in fisheries productivity, e.g., through the creation of compensation lakes. Offsetting strategies are becoming increasingly important for large-scale developments such as mining operations in the oil sands region; they allow for development while ensuring that the project has ‘no net loss’ in fisheries productivity. In 2012, omnibus Bill C-38 fundamentally changed large sections of the federal Fisheries Act. The focus of fisheries management was shifted from the protection of fish habitat in general to ensuring the ongoing productivity (FP) of fish important to commercial, recreational and aboriginal (CRA) fisheries. Further, the changes formalized the use of offsetting strategies to compensate for damage to fish caused by development. The changes marked the move from the fisheries habitat management program (FHMP) as implemented prior to 2012, to the fisheries protection program (FPP). The goal of the FPP is to “provide for the sustainability and ongoing productivity of commercial, recreational and Aboriginal fisheries”. Lack of standardized protocols and procedures following a shift of this magnitude could not only result in considerable additional expenses for industry, but also in less reproducible and so less reliable results. Rapid standardization of best practices and data collection methods would help ensure cost-efficient, meaningful and transferable data. Currently, these best management practices are being determined through an ongoing process involving Fisheries and Oceans Canada (DFO), industrial partners and government officials. The aim is to define a standard set of indicators for use under the FPP framework and assess which models may suitable for forming the link between data sets and long-term projections for whole-population productivity. The interpretation of the changes to the Fisheries Act has been subject to controversy, making concise and publically available information important. Numerous scientific advisory reports have been published by DFO. However, there is currently a shortage of documents that give an overview over the scientific background necessary to understand how the changes may affect management practices, taking into account knowledge gaps and limitations in terms of data collection techniques. In this report, we will review existing monitoring tools as well as how the changes in policies associated with the shift from the FHMP to the FPP may affect management protocols. Under the FHMP, the conceptual endpoint for assessing the impacts of development on fisheries was to achieve no net loss of the productive capacity of fish habitat (PC). Habitat was quantified mainly by area, and the success of an offsetting project was often determined mainly through acceptable installation. Methods in use under the FHMP provided only approximate values for PC. For a meaningful planning, measurement and monitoring protocol that can help ensure fisheries productivity under the FPP, it may be necessary to move away from the previous practice of managing fish habitat in Canada based on the use of FP as a theoretical concept only. As productivity in itself is difficult to measure directly, it is necessary to find appropriate indicators that can link changes in the components of productivity of individual fish or subsections of populations to changes in population-level fisheries productivity. We have compiled a list of indicators that may be used for estimating productivity of fisheries populations. Solid measurements of fisheries productivity require repeated monitoring protocols extended over multiple years as well as a broadening of the definition of habitat affected by development. The financially and ecologically prohibitive nature of obtaining comprehensive, long-term data sets may make models an essential tool for linking limited data on subsets of populations with whole-population productivity and long-term projections. However, the trade-off between strength of model predictions and quality and quantity of data may make it a challenge to strike the balance between data needs for accurate predictions and financial feasibility. In using knowledge-based standards for planning and executing compensation lake development, a key parameter to evaluate would be the carrying capacity of various compensation lake ecosystems. It may be a challenge to ensure an appropriate agreement between offsetting indicators and environmental assessment indicators, as established ecosystems are compared with populations in the process of establishing in a newly expanded habitat. On the other hand, lack of density dependence in the early establishment phase gives good possibilities for providing solid estimates of intrinsic growth rate of the populations within this specific habitat. Future research should be conducted for areas characterized by intensive development to create models that allow for robust estimates of productivity based on limited and specific indicators that are manageable to measure. As factors limiting fisheries productivity vary between species, habitats and regions, it is likely that this would have to occur through the development of models specific for the given habitats and geographical areas. If the drivers of the ecosystem in question are not well studied, the most cost-effective and ecologically sound way of implementing the FPP may be to adopt the management practices of the FHMP largely unaltered, but with the interpretive end goal shifted to FP. This would only require a mandatory inclusion of population level data in the monitoring protocols, and an extended monitoring period of several years. All of this constitutes protocols already in use under the FHMP. Though much work has been done on measuring and modelling the productivity of fish populations, it has proven difficult or impossible to find simple, reproducible techniques that can be applied across habitat types and ecosystems. In our opinion, the best predictors for fisheries productivity remain the quantity and quality of available fish habitat combined with abundance, size structure data and species composition within the given habitats.

MFT chemical additives and the "Goldilocks zone" of mixing

Year of Publication: 2012

Abstract:
An estimated 700 million m3 of mature fine tailings (MFT) have accumulated, and continue to accumulate, in a growing number of containment ponds. Various combinations of mechanical and chemical treatments have been proposed for reclaiming tailings ponds, but a common theme is that they involve a critical amount of mixing. If too little mixing energy is introduced, the chemical additives are not adequately dispersed into the tailings, resulting in poor performance. If too much mixing energy is added, the shear tears flocs apart, regardless of the chemistries used. The “Goldilocks zone” of proper mixing can be small and elusive, and missing it can severely hamper dewaterability. However, the chemistries employed can affect the size of this window. In this research, MFT samples were treated with different chemical additives. A rheometer equipped with a helical stirring shaft was used to record mixing speed and torque as a function of time, allowing mixing energy inputs to be carefully measured. It was observed that when high molecular weight ionic polymers were dosed into MFT, torque sharply rose, making it easier to overmix. Lower-molecular weight and nonionic additives, conversely, resulted in a gradual increase in torque, allowing for better mixing control. Blending additives selected from both groups can result in mature fine tailings that not only dewater, but also are tolerant of a broader range of mixing energies.

Microbial activity and mycorrhizal potential of four overburden types used in the reclamation of extracted oil sands

Year of Publication: 1983

Abstract:
Slender wheatgrass andjack pine were grown in the greenhouse in cores containing a bottom layer of extracted oil sands with four overburdens individually layered over the sand. The overburdens included a muskeg peat, two shallow mineral overburdens and a deep overburden. Mycorrhizal development, microbial respi- ration and biomass and the degree of decomposition of slender wheatgrass roots in litter bags were determined in each plant species-overburden combination. Both ecto- and vesicular-arbuscular (VA) mycorrhizal inoculum was present in all four overburdens. The symbionts of slender wheatgrass were the "fine endophyte" and Glomus aggregatum. VA development was very low in peat whereas plants in the shallow overburdens became heavily mycorrhizal. Infection did not spread from the overburden layer to roots in the tailing sand. Jack pine roots in the peat and two shallow overburdens were heavily infected after 4 months. The most common symbiont was an ascomycete known as the E-strain. Microbial respiration was highest in the peat and was not influenced by plant species. Microbial biomass was also highest in the peat and much lower in the mineral overburdens. Only in the peat was the amount of microbial biomass larger with slender wheatgrass than with jack pine. Slender wheatgrass roots decomposed most rapidly in the peat overburden and least rapidly in the deep overburden.

Microbial biodegradation of aromatic alkanoic naphthenic acids is affected by the degree of alkyl side chain branching

Year of Publication: 2011

Abstract:
Naphthenic acids (NAs) occur naturally in oil sands and enter the environment through natural and anthropogenic processes. NAs comprise toxic carboxylic acids that are difficult to degrade. Information on NA biodegradation mechanisms is limited, and there are no studies on alkyl branched aromatic alkanoic acid biodegradation, despite their contribution to NA toxicity and recalcitrance. Increased alkyl side chain branching has been proposed to explain NA recalcitrance. Using soil enrichments, we examined the biodegradation of four aromatic alkanoic acid isomers that differed in alkyl side chain branching: (4′-n-butylphenyl)-4-butanoic acid (n-BPBA, least branched); (4′-iso-butylphenyl)-4-butanoic acid (iso-BPBA); (4′-sec-butylphenyl)-4-butanoic acid (sec-BPBA) and (4′-tert-butylphenyl)-4-butanoic acid (tert-BPBA, most branched). n-BPBA was completely metabolized within 49 days. Mass spectral analysis confirmed that the more branched isomers iso-, sec- and tert-BPBA were transformed to their butylphenylethanoic acid (BPEA) counterparts at 14 days. The BPEA metabolites were generally less toxic than BPBAs as determined by Microtox assay. n-BPEA was further transformed to a diacid, showing that carboxylation of the alkyl side chain occurred. In each case, biodegradation of the carboxyl side chain proceeded through beta-oxidation, which depended on the degree of alkyl side chain branching, and a BPBA degradation pathway is proposed. Comparison of 16S rRNA gene sequences at days 0 and 49 showed an increase and high abundance at day 49 of Pseudomonas (sec-BPBA), Burkholderia (n-, iso-, tert-BPBA) and Sphingomonas (n-, sec-BPBA).

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